1. Field of the Invention
The present invention relates to a beam-index-type color display apparatus.
2. Description of the Related Art
There is known a beam-index-type color display apparatus which has no shadow mask. Such a beam-index-type color display apparatus comprises a two-dimensional screen composed of fluorescent stripes of three primaries, i.e., R (red), G (green), and B (blue), the fluorescent stripes being arranged at regular intervals in a horizontal scanning direction. Since the two-dimensional screen is scanned with a single electron beam, it is necessary to detect the horizontally scanning spot of the electron beam and feed back a signal indicative of the horizontally scanning spot in order to excite the fluorescent stripes in exactly timed relation to the light beam.
One conventional color display apparatus which has been proposed to meet the above requirement is shown in FIG. 1 of the accompanying drawings (see Japanese Patent Publication No. 61-61315). The known color display apparatus has a two-dimensional screen 33 which comprises fluorescent stripes 31 of R, G, B arranged at regular intervals in a horizontal scanning direction, and black stripes 32 each disposed between adjacent two of the fluorescent stripes 31, the black stripes 32 being made of a black light-shielding material. A metal backing layer 34 of aluminum is disposed over the entire surface of the screen 33. Index fluorescent stripes 35 are mounted on the metal backing layer 34 and spaced in the horizontal scanning direction at intervals or a pitch equal to 2/3, for example, of the pitch of one set of R, G, B fluorescent stripes 31. When the screen 33 is horizontally scanned with a single electron beam, the electron beam is applied to the fluorescent stripes 35 successively, which are then excited. The excited fluorescent stripes 35 emit light that is detected by a light detector 36 which then generates a signal to be fed back for synchronizing purpose.
The prior color display apparatus of the beam index type requires a vacuum system for generating an electron beam to scan the two-dimensional screen 33. Therefore, the color display apparatus is relatively heavy. Since the electron gun for emitting the electron beam and the screen 33 are positionally fixed with respect to each other, the size of the screen 33 cannot be altered, particularly, it cannot be increased.